System and method for interrogation radio-frequency identification

ABSTRACT

A system and method for communicating with contactless IC cards of multiple protocols and power levels includes generating a first alternating magnetic field with an interrogator for energizing a proximate IC card and receiving a data transmission from the IC card. A processor of the interrogator is configured to decode the received data transmission. The interrogator then generates a second alternating magnetic field having a different magnetic field strength than the first alternating magnetic field when failing to decode the data transmission being received from the IC card. The processor then attempts to decode a data transmission received from the IC card in response to the second alternating magnetic field.

STATEMENT OF RELATED APPLICATIONS

The present application may be considered to be related to co-pendingU.S. patent application Ser. No. 11/______ filed on even date herewith(Attorney Docket No. FAR-0006 (036399-010), in the name of inventorChristopher P. Nelson, entitled “System And Method For Multi-ProtocolRadio-Frequency Identification”, commonly owned herewith.

TECHNICAL FIELD

The present disclosure relates generally to radio-frequencyidentification (RFID) technology and more specifically to an RFIDinterrogator.

BACKGROUND

The development of RFID systems has been fueled by advances inintegrated circuit (IC) technology, which enables significantminiaturization of electronic devices, and recent growth in thepopularity of wireless communications, which provides a secure andreliable way for transferring information using RF signals. Typically,an RFID system includes an RFID interrogator (or reader) and one or moreRFID tags (or contactless IC cards). In operation, the RFID interrogatorgenerates an alternating magnetic field, which induces electric currentin a proximate RFID tag. The induced electric current provides enoughpower to the RFID tag to transmit a response signal to the RFIDinterrogator.

Due to relative simplicity and low cost of manufacturing, RFID systemshave gained a widespread application. For example, RFID technology iscommonly used for personal authentication in passports and other formsof ID. In the transportation sector, RFID cards are used to pay for theuse of public transportation and highways. In the retail environment,RFID tags are used for product tracking. In the banking industry, RFIDtechnology is embedded in debit and credit cards. In securityapplications, RFID cards are used to access secure areas or services. Inmedicine, RFID technology is used in human implants to monitor varioushealth conditions, monitor prescribed drugs and the like.

The growing demand for RFID products has resulted in development ofnumerous proprietary and non-proprietary RFID technologies. Theproprietary nature of some of these technologies often makes themincompatible with each other. For example, RFID systems manufactured bydifferent vendors may use custom communication protocols and dataformats and have different power requirements. Despite industry-wideefforts to standardize RFID technologies, there remain numerousincompatible RFID systems. Accordingly, there is a need for an RFIDinterrogator interoperable with various RFID tags, which may havedifferent protocols, data formats and power requirements.

OVERVIEW

Disclosed are a radio-frequency identification method and systeminteroperable with disparate RFID communication protocols, data formatsand power requirements. In one example embodiment, an IC card reader,such as RFID interrogator, includes a transmitter configured to generatean alternating magnetic field for energizing one or more proximate ICcards and transmit an IC card polling signal. The first alternatingmagnetic field may correspond to a first output power level. The IC cardreader further includes a receiver configured to receive a datatransmission from a proximate IC card. The IC card reader furtherincludes a processor configured to attempt to decode in real-time thedetected data transmission and generate a control signal when failing todecode the data transmission. In response to the control signal, thetransmitter configured to generate a second alternating magnetic fieldhaving a different magnetic field strength than the first alternatingmagnetic field, wherein the second alternating magnetic fieldcorresponds to a second output power level. In one embodiment, the firstalternating magnetic field is stronger than the second alternatingmagnetic field. In another embodiment, the first alternating magneticfield is weaker than the second alternating magnetic field.

In one example embodiment, the processor may be further configured torepeatedly alternate generation of a control signal thereby alternatinggeneration of the first alternating magnetic field and the secondalternating magnetic field and attempt to decode data transmissionsreceived from one or more IC cards following generation of eachalternating magnetic field. The processor may be further configured tocompute the number of decoded data transmissions following the firstalternating magnetic fields, and compute the number of data transmissiondecoded following the second alternating magnetic fields. The processormay be further configured to adjust a duration of the first output powerlevel and a duration of the second output power level as a function ofone of (i) the number of decoded data transmissions following the firstalternating magnetic fields and (ii) the number of decoded datatransmission following the second alternating magnetic fields.

Another example embodiment relates to a method for communicating withcontactless IC cards. The method includes generating a first alternatingmagnetic field for energizing a proximate IC card and receiving a datatransmission from a proximate IC card. The method further includesattempting to decode the data transmission being received from the ICcard. When failing to decode the data transmission being received fromthe IC card, generating a second alternating magnetic field having adifferent magnetic field strength than the first alternating magneticfield and again attempting to decode a data transmission being receivedfrom the IC card. In one embodiment, the first alternating magneticfield is stronger than the second alternating magnetic field. In anotherembodiment, the first alternating magnetic field is weaker than thesecond alternating magnetic field.

The method may further includes repeatedly alternating generation of thefirst alternating magnetic field and the second alternating magneticfield and attempting to decode data transmissions received from one ormore IC cards following generation of each alternating magnetic field.The method may further include computing the number of decoded datatransmissions following the first alternating magnetic fields, andcomputing the number of data transmission decoded following the secondalternating magnetic fields. The method may further include adjusting aduration of the first output power level and a duration of the secondoutput power level as a function of one of (i) the number of decodeddata transmissions following the first alternating magnetic fields and(ii) the number of decoded data transmission following the secondalternating magnetic fields.

Another example embodiment relates to a method for communicating withcontactless IC cards. The method includes generating a first alternatingmagnetic field for energizing a proximate IC card and transmitting an ICcard polling signal. The method further receiving a data transmissionfrom a proximate IC card and determining whether or not the datatransmission is being received in response to the polling signal. Whenthe data transmission is being received in response to the pollingsignal, attempting to decode the data transmission being received. Whenfailing to decode the data transmission being received, generating asecond alternating magnetic field having a different magnetic fieldstrength than the first alternating magnetic field.

The method may further include attempting to decode a data transmissionbeing received from the proximate IC card following generation of thesecond alternating magnetic field. The method may further includedetermining whether the data transmission being received before or afterexpiration of a predetermined time period following transmission of thepolling signal. The method may further include storing the received datatransmission in a memory and decoding the stored data transmission whenthe data transmission is not being received in response to the pollingsignal. The format of the data transmission may be determined bydetermining whether the data transmission includes one or more startbits, determining whether the data transmission includes one or moreparity bits, and/or determining whether the data transmission includesone or more cyclic redundancy check (CRC) bits.

In yet another embodiment a computer-readable medium comprisingcomputer-executable instructions for configuring operation of acontactless IC card interrogator includes instructions for selecting afirst output power level of the IC card interrogator and selecting asecond output power level of the IC card interrogator when the IC cardinterrogator fails to decode one or more data transmissions from aproximate IC card. The computer-executable instructions may furtherinclude instructions for selecting a duration of the first output powerlevel and a duration of the second output power level.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more examples ofembodiments and, together with the description of example embodiments,serve to explain the principles and implementations of the embodiments.

In the drawings:

FIG. 1 is a block diagram illustrating an example embodiment of an RFIDsystem.

FIG. 2 is a flow diagram illustrating an example embodiment of an RFIDinterrogation process having RTF and TTF operating modes.

FIG. 3 is a flow diagram illustrating an example embodiment of an RFIDinterrogation process having multiple power levels.

FIG. 4 is a flow diagram illustrating an example embodiment of an RFIDinterrogation process having combined RTF/TTF operating modes andmultiple power levels.

FIGS. 5-7 are flow diagrams illustrating example embodiments of datadecoding processes.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Example embodiments are described herein in the context of an RFIDcommunication system. Those of ordinary skill in the art will realizethat the following description is illustrative only and is not intendedto be in any way limiting. Other embodiments will readily suggestthemselves to such skilled persons having the benefit of thisdisclosure. Reference will now be made in detail to implementations ofthe example embodiments as illustrated in the accompanying drawings. Thesame reference indicators will be used to the extent possible throughoutthe drawings and the following description to refer to the same or likeitems.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

In accordance with this disclosure, the components, process steps,and/or data structures described herein may be implemented using varioustypes of operating systems, computing platforms, computer programs,and/or general purpose machines. In addition, those of ordinary skill inthe art will recognize that devices of a less general purpose nature,such as hardwired devices, field programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), or the like, may alsobe used without departing from the scope and spirit of the inventiveconcepts disclosed herein. Where a method comprising a series of processsteps is implemented by a computer or a machine and those process stepscan be stored as a series of instructions readable by the machine, theymay be stored on a tangible medium such as a computer memory device(e.g., ROM (Read Only Memory), PROM (Programmable Read Only Memory),EEPROM (Electrically Erasable Programmable Read Only Memory), FLASHMemory, Jump Drive, and the like), magnetic storage medium (e.g., tape,magnetic disk drive, and the like), optical storage medium (e.g.,CD-ROM, DVD-ROM, paper card, paper tape and the like) and other types ofprogram memory.

Turning now to FIG. 1, a block diagram illustrating one exampleembodiment of an RFID system 100 is shown. The RFID system 100 includesRFID interrogator 110 and a plurality of RFID tags 160 (160A, 160B,160C). The RFID interrogators 110 includes an RFID controller 120, whichincludes a processor 122 and memory 124. The interrogator 110 furtherincludes RF transmitter 130, which includes a modulator 132 and poweramplifier 134. The interrogator 110 further includes an RF receiver 140,which includes a demodulator 142 and power amplifier 144. Theinterrogator further includes one or more RF antennas 150. The diagramhas been simplified to include primarily elements of the system 100 thatwill be relevant to the discussion that follows. Those of ordinary skillin the art will readily identify other elements that might also beincluded as desired or required. The various elements may be alsoseparated, combined or reordered as desired or required. Other means ofimplementing the interrogator are also known to those of skill in theart and are not intended to be excluded.

In one example embodiment, an interrogator 110 includes an RFIDcontroller 120, which controls operation of various components ofinterrogator 110, such as transmitter 130 and receiver 140. Controller120 may be configured to select an operating mode of the interrogator110, determine an output power level of transmitted RF signals, decodedata transmissions received from the RFID tags 160, and perform otherfunctions known to those of ordinary skill in the art. In one exampleembodiment, controller 120 may be implemented as a 8-bit PIC®programmable microcontroller (available from Microchip Technology, Inc.of Chandler, Ariz.). In alternative embodiments, controller 120 may beimplemented at least in part with a general purpose microprocessor, afield programmable gate array, an application specific integratedcircuit (ASIC) or the like.

In one example embodiment, controller 120 includes a processor 122 and amemory 124. Processor 122 may store and execute program logic foroperating various components of the interrogator 110, decoding datatransmissions received from various RFID tags 160, performing arithmeticand logic operations and other functions. The processor 122 is coupledto memory 124 (which may be implemented as on-board memory), which maybe used to store executable program instructions and other data for useby processor 122 during decoding of RFID information. Memory 124 mayinclude volatile or non-volatile program memory, such as ROM (Read OnlyMemory), PROM (Programmable Read Only Memory), EEPROM (ElectricallyErasable Programmable Read Only Memory), FLASH memory, and other typesof magnetic and optical storage media for storing RFID information andother data.

In one example embodiment, interrogator 110 includes a RF transmitter130, which is operable to receive digital data from processor 122,modulate the receive data using modulator 132, amplify the modulatedsignal using power amplifier 134 and route the amplified RF signal toantenna 150. In addition, transmitter 130 is configured to generatealternating magnetic field for energizing IC cards proximate to theinterrogator 110. Modulator 132 may be configured to receive a data bitsequence from processor 122 and modulate a receive bit sequence on acarrier signal. The carrier signal may be generated by an oscillator(not shown) and have 13.56 MHz frequence in compliance with ISO/IEC14443 standard for contactless IC cards. Other frequencies may be used,if desired. Modulator 132 may be configured to use one or more of thevarious known signal modulation techniques, including amplitudemodulation (such as Manchester or QAM (Quadrature Amplitude Modulation)modulation), frequency modulation (such as FSK (Frequency-Shift Keying)modulation), or phase modulation (such as PSK (Phase-Shift Keying)modulation) and variants thereof.

RF transmitter 130 may further include a power amplifier 134 foramplifying a modulated data signal and routing it to the antenna 150,which radiates the amplified signal to proximate RFID tags. In oneexample embodiment, controller 120 may control an output power level ofamplifier 134. To that end, power amplifier 134 may be implemented as amulti-stage variable power amplifier, which may (in response to acontrol signal from RFID controller 120) increase/decrease its outputpower level by turning on/off one or more of its amplification stages.In alternative embodiments, the transmitter 130 may use othervariable-power amplification techniques known to those skilled in theart. In one example embodiment, amplifier 134 may vary its output powerlevel from 3.5 A/m to 12.5 A/m in 0.5 A/m increments. The desired outputpower range may be selected based on specific power requirements of oneor more RFID tags.

In one example embodiment, interrogator 110 includes an RF receiver 140,which is configured to receive data transmissions from antenna 150,demodulate the received data using demodulator 142, amplify thedemodulated digital data signal using power amplifier 144 and route theamplified signal to processor 122 for decoding. To demodulate a signal,demodulator 132 may use a PLL (Phase Lock Loop) (not shown) and areference signal generated by an oscillator (not shown) to synchroniseitself with the incoming data transmission and extract a digital datasignal from the carrier signal. Furthermore, demodulator 132 needs toknow the modulation type of the incoming data transmission, which, inmost cases, will be identical to the modulation type used by thetransmitter 132. The demodulated data signal is amplified and routed toprocessor 122.

In one example embodiment, interrogator 110 includes one or more RFantennas 150 for transmitting and receiving RF signals. In one exampleembodiment, antenna 150 may be implemented as a single mono-static RFantenna, which may transmit a signal coming from transmitter 130 as wellas receive a signal coming from a RFID tag 160. Switching betweentransmitting and receiving modes may require use of a circulator (notshown) that multiplexes the received and transmitted signals through asingle port. In another example embodiment, antenna 150 may beimplemented as a bi-static antenna, including two antennas, where oneantenna is dedicated to transmitting, and the other antenna is dedicatedto receiving. Use of a bi-static antenna can improve the sensitivity ofantenna 150, thereby improving the performance of interrogator 110.

In one example embodiment, RFID interrogator 110 has two operatingmodes: reader talk first (RTF) mode and tag talk first (TTF) mode. Inthe RTF mode, the interrogator 110 initiates a communication sessionwith an RFID tag by transmitting a polling signal, which may be detectedby RTF tags 160 located in the proximity of interrogator 110. RFID tag160 may process the received polling signal and respond to theinterrogator 110 with a response data transmission. In the TTF mode, anRFID tag 160 initiates a communication session when placed in proximityof interrogator 110 by either sending a beacon signal or starting theactual data transmission. In this mode, interrogator 110 listens for anysignals detected at the receiver 140. When a data transmission isdetected from a TTF tag 160, interrogator 110 attempts to decode itusing methods described hereinbelow. The interrogator 110 mayperiodically alternate between the two operating modes, thereby managingto read different types of RFID tags.

In one example embodiment, interrogator 110 may use different methodsfor decoding RTF and TTF data transmissions. RTF transmissions may bedecoded in real-time, because interrogator 110 may know the format ofthe data transmission in advance. In particular, an RTF datatransmission is send by the RTF tag 160 in response to a polling signaltransmitted by the interrogator 110. The polling signal may containinformation about communication protocol utilized by the interrogator110, such as a version number of the communication protocol, vendorinformation, data format information and the like. In this way, the RTFtag knows how to format its response data transmission, so it can bedecoded by interrogator 110 on the fly. In contrast, TTF transmissionsare initiated by RFID tags 160 and thus cannot be decoded in real-timebecause the format of the data transmission is not known to interrogator110 in advance. To that end, the interrogator 110 stores the entire TTFdata transmission in memory 124 and only then begins decoding of thestored data transmission, as discussed herein below.

Turning now to FIG. 2, an example embodiment of an RFID interrogationprocess 200 is illustrated in a flow diagram. At step 205, RFIDinterrogator enters RTF mode and sends a polling command. At step 210,the interrogator listens to a channel for a first predetermined periodof time, which is sufficiently long to receive a response from a RTF taglocated in the proximity of the RFID interrogator. In one exampleembodiment, the period of time may correspond to a frame delay time,which may vary between different communication standards. TheInternational Standards Organization (ISO) has adopted standard ISO/IEC14443-1:2000 entitled “Identification cards—Contactless integratedcircuit(s) cards—Proximity cards” as amended by ISO/EEC 1443-2:2001,ISO/IEC 14443-3:2001 and ISO/IEC 14443-4:2001. In accordance with thatstandard, which applies to many IC cards in use today, the ISO/IEC 14443standard frame delay time is set to 91.1 microseconds. If a datatransmission is received within the predetermined period of time, theRFID interrogator concludes that it comes in response to the pollingcommand from a proximate RTF RFID tag, step 215. The interrogator thendemodulates, amplifies and decodes in real time the data transmissionbeing received, step 220. The processor then extracts identificationinformation from the decoded bit sequence for further processing, step225.

If no data transmission was received in the first predetermined timeperiod, step 210, the RFID interrogator enters TTF mode, step 230. Inthe TTF mode, the interrogator listens to a channel for a secondpredetermined period of time, which may be arbitrarily selected by asystem administrator. In one example embodiment, the TTF mode may lastfor 300 milliseconds, step 235. If no data transmission was receivedduring the second predetermined time period, the RFID interrogator mayswitch back to the RTF mode, described above. If data transmission isdetected during the second time period, the interrogator concludes thatthe data transmission is coming from TTF RFID tag, step 245. Theinterrogator then demodulates the received data transmission and storesit in memory for further processing using algorithms describedhereinbelow, step 250.

In another example embodiment, interrogator 110 may be interoperablewith different power types of RFID tags, such as RFID tags that requirelower power and RFID tags that require higher power energizingalternating magnetic fields from the interrogator 110. For example,ISO/IEC 14443 standard limits the unmodulated field strength to between1.5 A/m minimum and 7.5 A/m maximum. Some tags that use variants of theISO/IEC 14443 standard may require alternating magnetic field of 12.5A/m to function properly, while other tags may require magnetic field of3.5 A/m only. Therefore, low-power RFID tags may be internallyoverdriven by interrogators having strong magnetic field and thus may beunreadable. In contrast, high-power RFID tags may not turn on properly,have insufficient read range, or have bit errors if not supplied withadequate power by the interrogator.

To accommodate different power type RFID tags, interrogator 110 may beconfigured to switch between different power levels by continuouslyadjusting its magnetic field strength until successful reading of aproximate RFID tag. In one example embodiment, interrogator may be setat low power level to generate alternating magnetic field of 3.5 A/m. Ifa tag 160 is read but errors are detected, the magnetic field strengthmay be increased in, for example, 0.5 A/m increments, by increasingtransmitter's output power, until the read is successful. In anotherembodiment, interrogator 110 may be set to high power level to generatealternating magnetic field of 12.5 A/m. If a tag 160 is read but errorsare detected, the magnetic field strength may be decreased by decreasingtransmitter's output power until the read is successful. Yet in anotherembodiment, interrogator 110 may be configured to continuously sweep theoutput power from low to high to low in a periodic manner, therebymanaging to communicate both with low and high power RFID tags.

In example embodiment, interrogator 110 may be configured to learn thepower types of RFID tags that come in contact with the interrogator 110and then adjust the duration of each output power level accordingly. Forexample, interrogator 110 may keep a running count of the number of RFIDtags of each power type read during a predetermined time period and thendwell at a specific output power level more often than other powerlevels. Depending on the interrogator's magnetic field strength when theRFID tag read occurs, interrogator 110 may classify the tag as high orlow power. For example, if the last 100 reads show 80 high power tagsand 20 low power tags, the interrogator 110 may set the output powerlevel bias towards high power tags, e.g. set dwell times to an 80% highpower and 20% low power duty cycle. In another example, interrogator 110may operate at high output power level and only decrease the outputpower when a data communication from a detected RFID tag has errors dueto requirement for lower power from the interrogator 110.

Turning now to FIG. 3, an example embodiment of a variable output powerRFID interrogation process is illustrated in a flow diagram. At step305, interrogator 110 generates an alternating magnetic field having apredetermined magnetic field strength, e.g., 12.5 A/m. The interrogatorlistens for a predetermine time period, such as 91.1 microseconds, fordata transmissions from proximate RFID tags, step 310. When a datatransmission is detected, processor 122 attempts to decode the datatransmission. If interrogator 110 fails to decode the data transmissiondue to one or more errors therein, step 315, the processor 122 mayselect another output power level, which may be higher or lower than theprevious output power level, and send a control signal to RF transmitter130 to adjust magnetic field strength accordingly, step 320. Inresponse, transmitter 130 generates an alternating magnetic field havinga different field strength, such as 7.5 m/A. Steps 305 through 320 maybe repeated for a predetermined time period, a predetermine number ofoutput power levels, or until a data transmission from a proximate RFIDtag 160 is decoded and output for further processing, step 325.

Once a data transmission from an RFID tag is decoded and output forfurther processing, step 325, the interrogator may be configured torepeat the interrogation cycle in steps 305 through 325 for apredetermined period of time, step 330, predetermined number ofinterrogation cycles, or predetermined number of successful tag reads.During interrogation, the processor 122 may keep a running count of thenumber of RFID tags read at each power level, step 335. Once the totalnumber of RFID tag read for each power level is computers, the processormay adjust duration of each output power level to correspond to thenumber of tags read at the given output power level. For example, ifduring 24 hour time interval, the interrogator read 80 high power tagsand 20 low power tags, the interrogator 110 will set the output powerlevel bias towards high power tags, e.g. set dwell times to an 80% highpower and 20% low power duty cycle.

In another example embodiment, interrogator 110 may be configured tooperate at multiple power levels while supporting both TTF and RTF tags.FIG. 4 is a flow diagram of example embodiment of RFID interrogationprocess having combined multiple power levels and TTF/RTF capabilities.At step 405, interrogator 110 generates an alternating magnetic fieldhaving a predetermined magnetic field strength for energizing proximateRFID tags. The interrogator then enters RTF mode and sends a pollingcommand, step 410. The interrogator then listens for a predeterminedtime period, such as 91.1 microseconds, for data transmissions fromproximate RFID tags, step 415. If data transmission is detected duringthis time period, the interrogator may enter a TTF mode, step 420, andlisten for a predetermined time period for data transmissions from TTFtags, as will be described in greater detail herein with reference toFIGS. 5-7.

If a data transmission from a RTF tag is detected, step 415, theinterrogator attempts to decode it, step 425. If interrogator 110 failsto decode the data transmission due to one or more errors therein, theprocessor 122 selects another output power level, which may be higher orlower than the previous output power level, and send a control signal toRF transmitter 130 to adjust magnetic field strength accordingly, step435. In response, transmitter 130 generates an alternating magneticfield having a different field strength, step 440. Steps 415 through 440may be repeated for a predetermined time period, a predetermine numberof output power levels, or until a data transmission from a proximateRFID tag 160 is detected, decoded and output for further processing,step 445. Once a data transmission from TTF tag or RTF tag has beenprocessed, interrogator 110 may be configured to repeat theinterrogation cycle in steps 405 through 445.

As indicated above, in the TTF mode, RFID interrogator 110 is configuredto interrogate RFID tags 160 that use one or more variations of theISO/IEC 14443 standard for contactless IC cards. Depending on thevariation used by RFID tag 160, the data transmitted by the tag 160 maybe formatted to contain one or more start bits (S), one or more databits (D), odd (O) or event (E) parity bits and cyclic redundancy check(CRC) bits (C). Below are several examples of bit sequences thatinterrogator 110 may be able to decode:

S DDDDDDDDO DDDDDDDDO CCCCCCCCO CCCCCCCCO (standard ISO/IEC 14443-A bitsteam)

DDDDDDDD DDDDDDDD (no start bit, no parity bits, no CRC)

DDDDDDDD DDDDDDDD CCCCCCCC CCCCCCCC (no start bit, no parity bits, CRC)

S DDDDDDDDO DDDDDDDDO (start bit, odd parity bits, no CRC)

S DDDDDDDDE DDDDDDDDE (start bit, even parity bits, no CRC)

S DDDDDDDDE DDDDDDDDE CCCCCCCCE CCCCCCCCE (start bit, even parity bits,and CRC)

In order to decode these and other bit sequences, the RFID interrogatormay use the following decoding algorithm: First, RFID interrogatorcounts the number of bits in the received bit sequence to see if thereis a start bit or not. Second, the interrogator checks each byte to seeif there is even, odd or no parity bits. Third, the interrogator checksfor the presence of a 16 bit CRC sequence. Once all of these parametersare determined the data is output in the corresponding format. Thisallows the interrogator to read tags that are fully ISO/EEC 14443compliant as well as RFID tags that use a TTF variant of the ISO/IEC14443 communication standard. Each of the above data processing stepswill be described in a greater detail hereinbelow with reference toFIGS. 5-7.

Turning now to FIG. 5, an example embodiment of a process 500 fordetermining the presence of one or more start bits in the RFID datatransmission is illustrated in flow diagram form. At step 505, aprocessor in the RFID interrogator calculates the total number of bitsin the received data transmission. The processor then determines if thetotal number of bits in the data transmission is divisible by 8 withoutremainder, step 510. If the total number of bits is divisible by eightwithout remainder, the processor concludes that there is no start bit inthe data transmission, step 515. If the total number of bits isdivisible by eight with remainder of 1, step 520, the processorconcludes that there is a start bit, step 525, and it is removed fromthe bit sequence, step 330. If the total number of bits is not evenlydivisible by eight, step 502, the processor then checks if the totalnumber of bits is evenly divisible by 9, step 535. If the total numberof bits is divisible by nine without remainder, the processor concludesthat there is no start bit in the data transmission, step 540. If thetotal number of bits is divisible by nine with remainder of one, step520, the processor concludes that there is a start bit, step 525, and itis removed, step 530.

The table below illustrates examples of operation of the algorithm ofFIG. 5.

Number Divisible Divisible of bits by 8? by 9? Remainder of 1?Conclusion 37 No No Yes when divided by 9 Start bit 36 No Yes Don't careNo start bit 32 Yes No Don't care No start bit 35 No No No Erroneous 33No No Yes when divided by 8 Start bit

The following are two examples of operation of the algorithm of FIG. 5.

S DDDDDDDDO DDDDDDDDO CCCCCCCCO CCCCCCCCO

Total number of bits received is 37, which does not divide evenly by 8or by 9. When divided by 9 there is a remainder of 1, therefore thefirst bit is a start bit.

DDDDDDDDO DDDDDDDDO CCCCCCCCO CCCCCCCCO

Total number of bits received is 36, which divides evenly by 9, thusthere is no start bit.

Once the start bit is removed from the bit sequence, the processor maycheck parity of the data transmission. FIG. 6 shows an exampleembodiment of a process 600 for determining the parity of the datatransmission. For the parity check the number of bits (minus the startbits) is divided by 8 and by 9. If the number of bits divides evenly by8 and not by 9, steps 605 and 610, the processor concludes that there isno parity, step 615. If the number of bits divides evenly by 9 and notby 8, steps 605 and 620, the processor concludes that there is parity,step 630. If the number of bits divides evenly by 8 and by 9, step 605and 610, the processor may do additional checking, step 635, asdescribed in the examples below. If the number of bits does not divideevenly by 8 or 9, steps 605 and 620, the data is erroneous, step 625,and may be discarded.

If parity is found, the processor may then check if it is even or odd.In order to do that, the processor checks each byte to see what parityis used. If all bytes use odd parity bits, step 640, the parity is setto odd, step 645, and the parity bits may be removed from the bitsequence, step 650. If all bytes use even parity bits, step 655, theparity is set to even, step 660, and the parity bits may be removed fromthe bit sequences, step 650. If there is a mix of even and odd paritybits, then the processor concludes that there are one or more bit errorsand the data sequence may be discarded, step 625.

The table below illustrates examples of operation of the process of FIG.6.

Number Divisible Divisible of bits by 8? by 9? Conclusion 36 No Yes Hasparity bits 32 Yes No No parity bits 72 Yes Yes Additional check neededto determine if there are parity bits 37 No No Erroneous

The following are three examples of operation of the process of FIG. 6.

DDDDDDDDO DDDDDDDDO CCCCCCCCO CCCCCCCCO

Total number of bits received is 36, which divides evenly by 9 and notby 8, so the processor determines that there is parity. The processormay then check the bit sequence and find all bytes that use odd parity,so that parity is set to odd.

DDDDDDDD DDDDDDDD CCCCCCCC CCCCCCCC

Total number of bits received is 32, which divides evenly by 8 and notby 9, so the processor determines that there is no parity.

DDDDDDDDO DDDDDDDDO DDDDDDDDO DDDDDDDDO

DDDDDDDDO DDDDDDDDO CCCCCCCCO CCCCCCCCO

Total number of bits received is 72, which divides evenly by 8 and by 9,so the processor must take every ninth bit of the bit sequence and checkit for even and odd parity. In this case every 9^(th) bit is found to bean odd parity bit, thus the parity is set to odd.

Once one or more parity bits are removed, the processor may determinewhether the data transmission includes one or more cyclic redundancycheck (CRC) bits. FIG. 7 illustrates an example embodiment of a process500 for performing a cyclic redundancy check. At step 705, the processormakes an assumption that last 2 bytes of the data transmission are CRCbytes until proven otherwise. The processor then performs a CRC checkusing methods known to those skilled in the art, step 710. If the CRCcompletes successfully, then the last 2 bytes are considered to be CRCbytes, step 720. The processor removes the CRC bytes, step 725, andoutputs the remaining data bytes containing identification information,step 730. If the CRC does not check out, then the last 2 bytes areconsidered to be data bytes, step 715, and the processor outputs theremaining data bytes containing identification information, step 730.

The following are two examples of operation of the algorithm of FIG. 7.

DDDDDDDD DDDDDDDD CCCCCCCC CCCCCCCC

The last 2 bytes are assumed to be CRC bytes and a CRC calculation isdone. In this case the CRC passes.

DDDDDDDD DDDDDDDD DDDDDDDD DDDDDDDD

The last 2 bytes are assumed to be CRC bytes and a CRC calculation isdone. In this case the CRC will fail and the last 2 bytes are taken asdata bytes.

In one example embodiment, operating modes and output power levels ofinterrogator 110 may be configured using a software executed on acomputer, which can be connected to the interrogator 110 via aninterface (not depicted in FIG. 1), such as a parallel port, serial portor network card. The software may include instructions for selecting afirst output power level of the IC card interrogator and selecting asecond output power level of the IC card interrogator when the IC cardinterrogator fails to decode one or more data transmissions from aproximate IC card. The software may also be used to select duration ofthe first output power level and second output power level. The softwaremay also specify duration of the RTF and TTF modes and other parameter.

Note that cryptographic encoding of identification data stored on the ICmay be used in accordance with any of the known standards and processesavailable to those of skill in the art.

While embodiments and applications have been shown and described, itwould be apparent to those skilled in the art having the benefit of thisdisclosure that many more modifications than mentioned above arepossible without departing from the inventive concepts disclosed herein.The invention, therefore, is not to be restricted except in the spiritof the appended claims.

1. A method for communicating with contactless IC cards, the methodcomprising: generating a first alternating magnetic field for energizinga proximate IC card, wherein the first alternating magnetic fieldcorresponds to a first output power level; receiving a data transmissionfrom a proximate IC card; attempting to decode the data transmissionbeing received from the IC card; generating a second alternatingmagnetic field having a different magnetic field strength than the firstalternating magnetic field when failing to decode the data transmissionbeing received from the IC card, wherein the second alternating magneticfield corresponds to a second output power level; and again attemptingto decode a data transmission being received from the IC card.
 2. Themethod of claim 1, wherein the first alternating magnetic field isstronger than the second alternating magnetic field.
 3. The method ofclaim 1, wherein the first alternating magnetic field is weaker than thesecond alternating magnetic field.
 4. The method of claim 1, furthercomprising: repeatedly alternating generation of the first alternatingmagnetic field and the second alternating magnetic field; and attemptingto decode data transmissions received from one or more IC cardsfollowing generation of each alternating magnetic field.
 5. The methodof claim 4, further comprising: computing the number of decoded datatransmissions following the first alternating magnetic fields; andcomputing the number of data transmission decoded following the secondalternating magnetic fields.
 6. The method of claim 5, furthercomprising: adjusting duration of the first output power level andduration of the second output power level as a function of one of (i)the number of decoded data transmissions following the first alternatingmagnetic fields and (ii) the number of decoded data transmissionfollowing the second alternating magnetic fields.
 7. A method forcommunicating with contactless IC cards, the method comprising:generating a first alternating magnetic field for energizing a proximateIC card; transmitting an IC card polling signal; receiving a datatransmission from a proximate IC card; determining whether or not thedata transmission is being received in response to the polling signal;attempting to decode the data transmission being received when the datatransmission is being received in response to the polling signal; andgenerating a second alternating magnetic field when failing to decodethe data transmission being received, the second alternating magneticfield having different magnetic field strength than the firstalternating magnetic field.
 8. The method of claim 7, furthercomprising: attempting to decode a data transmission being received fromthe proximate IC card following generation of the second alternatingmagnetic field.
 9. The method of claim 8, wherein the first alternatingmagnetic field is stronger than the second alternating magnetic field.10. The method of claim 8, wherein the first alternating magnetic fieldis weaker than the second alternating magnetic field.
 11. The method ofclaim 8, wherein determining whether or not the data transmission isbeing received in response to the polling signal comprises determiningwhether the data transmission being received before or after expirationof a predetermined time period following transmission of the pollingsignal.
 12. The method of claim 11, further comprising: storing thereceived data transmission in a memory and decoding the stored datatransmission when the data transmission is not being received inresponse to the polling signal.
 13. The method of claim 12, whereindecoding the data transmission stored in the memory includes determiningformat of the stored data transmission includes: determining whether thedata transmission includes one or more start bits; determining whetherthe data transmission includes one or more parity bits; and determiningwhether the data transmission includes one or more cyclic redundancycheck (CRC) bits.
 14. A system for communicating with contactless ICcards, the system comprising: a transmitter configured to generate afirst alternating magnetic field for exciting a proximate IC card,wherein the first alternating magnetic field corresponds to a firstoutput power level; a receiver configured to detect a data transmissionfrom a proximate IC card; and a processor configured to attempt todecode in real-time the detected data transmission, and generate acontrol signal when failing to decode the data transmission, wherein inresponse to the control signal the transmitter is configured to generatea second alternating magnetic field having a different magnetic fieldstrength than the first alternating magnetic field, wherein the secondalternating magnetic field corresponds to a second output power level.15. The system of claim 14, wherein the first alternating magnetic fieldis stronger than the second alternating magnetic field.
 16. The systemof claim 14, wherein the first alternating magnetic field is weaker thanthe second alternating magnetic field.
 17. The system of claim 14,wherein the processor is configured to repeatedly alternate generation acontrol signal thereby alternating generation of the first alternatingmagnetic field and the second alternating magnetic field; and attempt todecode data transmissions received from one or more IC cards followinggeneration of each alternating magnetic field.
 18. The system of claim17, wherein the processor is configured to compute the number of decodeddata transmissions following the first alternating magnetic fields; andcompute the number of data transmission decoded following the secondalternating magnetic fields.
 19. The system of claim 18, wherein theprocessor is configured to: adjust duration of the first output powerlevel and duration of the second output power level as a function of oneof (i) the number of decoded data transmissions following the firstalternating magnetic fields and (ii) the number of decoded datatransmission following the second alternating magnetic fields.
 20. Logicencoded in one or more tangible media for execution and when executedoperable to: select a first output power level of a contactless IC cardinterrogator; select a second output power level of the IC cardinterrogator when the IC card interrogator fails to decode one or moredata transmissions from a proximate IC card; and select a duration ofapplication of the first output power level and a duration ofapplication of the second output power level.